Check out these two really useful articles. Jeff Carlson has an ebook called Take Control of Your iPhone Apps, and in this article on TidBITs he gives what he feels are the top 7 tips from the ebook. The first tip, for example, tells you how to silence an incoming call and direct it to voicemail. Also, Ted Landau has an ebook titled Take Control of iPhone OS 3. And this excerpt on MacWorld tells you everything you need to know about the iPhone backup.